“I didn’t mean for it to get larger, but the climax that I pitched was completely unhinged and nobody said no, so that’s that.”

We caught up with the director on the film’s lavish Shepperton set in May last year to talk about how he planned to up the ante for the sequel to the most successful superhero film of all time.

Here’s what we found out.

Love is in the air (maybe)

The first official poster for ‘Age of Ultron’, which was unveiled earlier this week, boasts more A-list stars than the presenter roster at the Oscars. It’s a hard enough task for the graphic designer to squeeze all the stars onto one poster, so making sure all the actors are properly serviced in the script sounds like a gargantuan task.

While Whedon didn’t tell us how each role would be pumped for Age of Ultron, he did hint that Scarlett Johansson and Mark Ruffalo’s characters — Black Widow and the Hulk, respectively — have “a great deal to do” in the new film.

Even more intriguingly, Ruffalo indicated that a romance might on the cards for his character, saying Banner could be “finding love at some point.” The first trailer indicates that said romance could be between Hulk and Widow, as the pair can be seen enjoying a tender moment during the Johannesburg-set Hulkbuster sequence. Could the pitter-patter of superhero feet be on the horizon?

It will be emotional

“The biggest thing for me [in ‘Avengers: Age of Ultron’] is to go deeper with the characters,” the writer-director explained.

“There are new characters, there are more characters, but the troupe I have from the first movie is so amazing that I want to get in their heads, and this movie is letting me do that in a way I couldn’t in the first one.

“Now that people accept the reality where Thor, Iron Man and all these guys hang out, I can now bend that reality. I’ve got Quicksilver and I’ve got Scarlet Witch and they have very different ways of looking at the world, looking at The Avengers and different powers. So that visually and emotionally, we can go to a place that we didn’t have access to the first time.”

It’s partly a “woman’s picture”

If ‘Captain America: The Winter Soldier’ was a political thriller — and ‘Ant-Man’ is a heist film — in what genre does Whedon think ‘Age of Ultron’ belongs?

“To me, adventure film is the best way to put it,” he says. “Then science fiction, action, western, war, woman’s picture, horror movie … I’m not kidding; every single one of those things is in there.”

The finale will feature hundreds of Ultrons

Whedon wouldn’t elaborate on what the finale will look like — or where it takes place in the Marvel world —but one thing’s clear: It’s likely to involve a huge battle between the Avengers and Ultron’s clone army, as hinted at in early concept art from the film.

“I knew before I made the first film that Ultron needed be in the second one, along with Scarlet Witch and Quicksilver as well,” the writer-director said. “The way I approach a story is that I find these moments by thinking, ‘You know what I need to see?’ And generally if they work, you go from there.”

“You know they’re going to fight Ultron,” Whedon said. “You know Ultron has a tendency to build hundreds of Ultrons. So that’s going to lead you in a certain direction, but the hard work of the thing is making sure everyone feels serviced and integrated. So, in the beginning it’s fun. You’re thinking, ‘What would be fun, what would be cool?’”

The ending will have repercussions

While the first film was all about building this world, it seems the sequel is set to tear it all back down again.

“The whole movie [‘Age of Ultron’] is a process of changing everything and keeping everything the same. You want to hit all the things that made people love the first movie, but you also want to make something new or why are you here,” Whedon explains.

“I don’t want to make The Avengers again - I did that one time. With the ending it was important for me that we felt a progression. We didn’t just feel, ‘well, no problem, we cleaned that up!’ because that’s an episode of television. That’s not a film. This film, there’s more at stake and we take that seriously.”

Whedon was “much more focused” second time around

The ambitious globetrotting production visited South Africa, South Korea and Italy before coming to Shepperton, indicating that Whedon has been given carte blanche to do everything in his powers to top 2012’s hugely successful ‘The Avengers’.

This is some task considering the first film took $1.5bn at the global box office, but despite the pressure on his shoulders, Whedon says he’s much more chilled out this time around, mainly because people know what to expect from him on set.

“I’m having such a good time. I think people are a little more relaxed. I had a great crew in the first one but on this one, we all know what movie we’re making, in a way that nobody really knew when we started the first one, except for me, my editor, Kevin Feige and Jeremy Latchem.

“There’s a lot of trust, I myself just feel much more focused. I want every frame of this to be as good as it can be: as luscious, as interesting, and deep and funny as possible.

“There were a lot things that I couldn’t really focus on the first time because I just had to get the ‘whole’ into existence. Now I feel much better about this experience. I’m a happier person. It has a nothing to do with the Avengers but it’s extremely convenient for everyone around me.”

‘Avengers: Age Of Ultron’ is coming to UK cinemas on 23 April, before its global release on 1 May.